The present invention relates to a device for connecting adjacent turbine blades of turbine wheel such as steam turbines, gas turbines and so forth.
The specification of the U.S. Pat. No. 3,302,925 discloses a device for connecting adjacent turbine blades, particularly long turbine blades which is twisted over the entire lengths from the base to the end, of the turbine wheel in a vibration damping manner. In this known connecting construction, each turbine blade is provided with holes at the leading and trailing edges of the radially outer end thereof. A turbine blade cover having horizontal projections from both sides thereof, one of these horizontal projections being fitted in the hole of the trailing edge of the preceding turbine blade and caulked firmly therein, while the other projection is loosely received by the hole in the leading edge of the following moving blade, thereby to connect these two turbine blades.
Various studies have been made as to the behaviour of the turbine blades connected by the above-explained conventional connecting device. It has become clear, as a result of these studies, the turbine is seriously affected by a phenomenon of untwisting of the turbine blades due to the centrifugal force during operation of the turbine.
More specifically, during the operation of the turbine, a centrifugal force is applied to each turbine blade to generate an untwisting force or moment M on the turbine blade. This untwisting moment M is born by a counter moment M produced in the turbine blade cover by which the turbine blades are restricted. Namely, the untwisting of the turbine blade is restricted by the presence of the horizontal projections of the associated turbine blade cover. This means that an excessively large force is applied to the projections of the turbine blade cover, as well as a large bending moment. In consequence, there is a fear that the projections may be broken during the rotation of the turbine blade wheel, resulting in a serious accident. Thus, the conventional construction for connecting the turbine blades involves a serious problem concerning the reliability of the turbine blades.